US20120211195A1

US20120211195A1 - Control for Geothermal Heating System

Info

Publication number: US20120211195A1
Application number: US13/399,825
Authority: US
Inventors: Lorne R. Heise; Fraser F. Newton; David S. Lamb
Original assignee: Individual
Current assignee: Heat Line Corp
Priority date: 2011-02-18
Filing date: 2012-02-17
Publication date: 2012-08-23
Also published as: CA2827295A1; WO2012155258A1

Abstract

A geothermal energy transfer system has a heat transfer loop associated with a heat pump and a heat absorption loop to circulate fluid through an energy source, such as the ground or body of water. The loops are connected through a reservoir and each loop has a circulating pump to circulate fluid through respective loops. The flow rates of the pumps are selected to optimise energy transfer in each loops and differences in the flow rates are absorbed in the reservoir.

Description

FIELD OF THE INVENTION

The present invention relates to geothermal energy transfer systems.

SUMMARY OF THE INVENTION

It is well known to use a heat pump to transfer energy between a consumer of energy, such as a building, and a source of energy such as the surrounding environment. The heat pump uses a closed cycle that passes a refrigerant through an expansion phase, that requires the absorption of external energy, and a compression phase, which rejects energy to the building. In order to supply energy to a particular location, the rejected heat is transferred in to the heating system of that location and the energy required to effect the expansion of the refrigerant is absorbed from an external source. Similarly, when heat is to be extracted from the location, the location acts as a source and supplies the energy for the expansion of the refrigerant and the heat generated during compression is rejected to the surrounding environment that acts as a consumer.
The environment may be the air itself, as is the Case with traditional air conditioning units or heat pumps. However, such an arrangement has a poor efficiency due to fluctuations in the air temperature.
A preferred external source has a substantially constant temperature and the ground or large body of water are typically used. It is therefore known to provide a heat exchange loop between the heat pump and such a source so that heat may be absorbed in to the loop to supply energy to the heat pump or may be rejected from the loop to remove energy from the heat pump. The loops are typically an extensive run of pipe containing a saline, glycol or ethyl alcohol based heat exchange fluid. The pipe is buried in a trench between one or two meters below the normal surface. At that depth, the earth is at a substantially constant temperature and provides an energy source to either provide energy to or absorb energy from the heat transfer fluid because of the temperature differential between the heat exchange fluid and the surrounding.
Where available, a large body of water may be used as the energy source. The heat transfer loop is placed in the water and heat transfer fluid circulated through the loop.
The heat exchange loop is typically closed to isolate the heat transfer fluid from the environment. To compensate for losses of fluid and changes in the condition of fluid, a flow centre is placed in the heat exchange loop to subdivide the heat exchange loop in to a heat transfer loop and a heat absorption loop.
In a non-pressurized system, the flow centre acts, as a reservoir for heat transfer fluid. In a pressurized system, a dedicated reservoir is not provided as the system is typically charged with air after filling. In both applications, the flow center is usually placed between the loop that passes fluid through the heat pump (the heat transfer loop) and the loop that passes fluid through the ground or water loop (the heat absorption loop). A pump circulates the heat transfer fluid through the heat transfer loop and returns it to a manifold from which the heat absorption loop is supplied.
These arrangements typically size the circulating pump to maintain a turbulent flow through the heat transfer loop. However, such an arrangement has been found to introduce a loss of efficiency in the overall performance of the energy transfer system.
It is therefore an object of the present invention to obviate or mitigate the above disadvantages.
In general terms, an energy transfer system includes a first loop to circulate fluid through a heat pump and a second loop to circulate fluid through a geothermal energy source. Each of the loops is connected to a flow center to provide a reservoir of fluid for circulation. A respective pump is connected in each of said loops to establish respective flow rates of fluid in each of said loops, with balance flow being provided by the flow center.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way example only with reference to the accompanying drawings in which:

FIG. 1 is a schematic representation of an energy transfer system;

FIG. 2 is a perspective view of a flow center;

FIG. 3 is a schematic representation of flow through the flow center of FIG. 2;

FIG. 4 is a view, similar to FIG. 2 of an alternative flow center;

FIG. 5 is a schematic representation of flow through the flow center of FIG. 4;

FIG. 6 is a further embodiment of the energy transfer system;

FIG. 7 is a side elevation of a further embodiment of flow centre;

FIG. 8 is a section on the line VIII-VIII of FIG. 7;

FIG. 9 is a section on the line IX-IX of FIG. 8.

FIG. 10 is a flow chart showing a first control strategy for operation of the heating system of FIG. 1,

FIG. 11 is a flow chart showing a second control strategy for operation of the heating system of FIG. 1 in a heating mode, and

FIG. 12 is a flow chart showing the second control strategy for operation of the heating system of FIG. 1 in a cooling mode.

DETAILED DESCRIPTION OF THE INVENTION

Referring therefore to FIG. 1, a building 10 has a heating and cooling system 12 to distribute heat through the building or to remove heat from the building. The heat distribution system may be an air circulating system, or a water circulating system that transfers heat between different areas of the building and a heat source. The heating and cooling system 12 includes a heat exchanger 14 that cooperates with a heat exchanger 16 to transfer heat between a heat pump 18 and the building 10.
The heat pump 18 is of conventional construction and includes a heat exchanger 20 connected in a refrigerant loop 19 to the heat exchanger 16 through a throttle valve 22 and a compressor 24. Expansion of a refrigerant through the throttle valve 22 causes heat to be absorbed in to the refrigerant and compression of the refrigerant through the pump 24 causes heat to be rejected.
The heat exchangers 16 and 20 absorb or reject the heat depending upon the mode of the operation of the refrigerant cycle. A reversing valve 23 reverses the flow direction to allow the heat pump 18 to function in a heating mode to supply heat to the building, or a cooling mode in which heat is extracted from the building 10. A thermostat 27 and controller 25 is incorporated in to the system 12 to control operation and maintain the required temperature in the building 10.
The heat exchanger 20 cooperates with a further heat exchanger 26 to transfer heat between the refrigerant loop 19 and a heat transfer loop indicated at 28. The heat transfer loop 28 includes a pump 30 that circulates a heat transfer fluid, typically a saline, glycol or ethyl alcohol based mixture, through a return pipe 32 and a supply pipe 34.
The pipes 32, 34 are connected in series with a pair of header pipes 36, 38, one of which, 36 acts as a supply and the other, 38 acts as a return. The header pipes 36, 38 that are connected to opposite sides of a heat transfer unit 40 to provide a heat absorption loop 41. The heat transfer unit 40 may be a loop or multiple loops connected in parallel, to the header pipes 36, 38. The loop is buried in the ground or under water, or, preferably, is a self contained heat transfer unit of the type more fully described, in U.S. patent application 61/367,166, and the contents of which are incorporated herein by reference. The loops may also include loops to auxiliary heat consumers, such as a pool or spa, if required and as shown in FIG. 6, with a suffix ‘b’ for clarity. A pump 42 is connected in the header pipe 36 to circulate fluid through the heat absorption loop 41 defined by the pipes 36,38 and the heat transfer unit 40.
A flow center 44 is connected in parallel with the pipes 36, 38 and 32, 34 through stub pipes 46. The flow center 44 is seen more fully in FIG. 2 and, in its simplest form, comprises a cylindrical housing 50 sealed at its lower end. A cap 52 with a vent valve 54 is fitted to the housing 50 to provide venting to accommodate expansion and contraction of fluid in the fluid circulation loops 28, 41. The stub pipes 46 are connected on diametrically opposite sides of the housing 50. In the case of the pressurized configuration, the vent valve 54 is replaced with an air valve allowing the system to be pressurized. The Cap 52 is installed as to seal the system.
In operation, the heat transfer loop 28 and the heat absorption loop 41 are filled with fluid through filling the housing 50. The vent 54 allows for venting of air from the system and a cap 52 for adding/replenishing fluid during/after initial installation. The pumps 30 and 42 operate to circulate fluid through the heat exchanger 26 and through the heat exchanger 40. The pump 30 is sized to provide a turbulent flow through the heat transfer loop 28 at a rate that maximizes heat transfer between the heat exchangers 26 and 20. The rate required to attain optimum heat transfer will vary in different design conditions but for a supply of fluid at a particular temperature an optimum rate can be determined, from operating characteristics of the heat pump 18.
For a given heat transfer rate into the building 10, and with a design temperature of the heat transfer fluid and the known characteristics of the heat exchanger 26, an appropriate flow rate of the fluid passing through the heat exchanger 26 can be determined. Frequently, the design temperature and flow rates are specified by the manufacturer of the heat pump. For example, with a Geostar Model GT064, a nominal heat transfer of 27100 Btu/hr is specified with a flow rate of 16 US gpm and an assumed entering water temperature of 20° F. Correction tables are provided to compensate for different entry water temperatures (EWT).
Similarly, the pump 42 is sized to provide a circulation through the heat absorption loop at a rate that optimizes the transfer of energy between the heat exchanger 40 and the surroundings. Again this will depend upon the particular design conditions but an optimum flow rate can be attained, taking into account the temperature of the heat source, the thermodynamic properties of the fluid and the heat transfer characteristics of the heat transfer unit 40.
For the same thermal load, the heat absorption rate from the surroundings through the heat exchanger 40 may require a different flow rate through the heat absorption loop 41 to that in the heat transfer loop, 28.
The pumps 30, 42 can then be sized to provide those respective flow rates. Preferably, each of the pumps 30, 42 are variable flow rate pumps that can be adjusted to increase or decrease the flow rate to suit particular control strategies. Alternatively, one of the pumps 30, 42 may be a fixed capacity and the other variable to permit adjustment of the respective flow rates. If a steady condition is anticipated then both pumps may be of fixed flow rating for the anticipated conditions in the respective loop. However, as will be explained more fully below, the ability to adjust the flow rates may be used advantageously in the operation and control of the heating and cooling system 12.
As illustrated in FIG. 3, the flow center 44 operates as a reservoir to receive excess fluid from the heat absorption loop 41 and supply a balancing fluid back into that loop through respective ones of the stub pipes 46. Typically, it is found that the flow rate through the heat absorption loop 41 is greater than that required in the heat transfer loop and so the flow center 44 receives fluid from, and delivers fluid to, the heat absorption loop 41. In FIG. 3, the flow required through the heat transfer loop 28 is denoted by Y and the flow rate required in the heat absorption loop 41 is X+Y. The flow center 44 thus receives X gallons per minute from the heat absorption loop 41 through one of the stub pipes 46 acting as an inlet and similarly delivers X gallons per minute to that loop 41 from the other stub pipes 56 acting as an outlet to supply the pump 42. In one installation with an eighteen kilowatt heat load, it has been found that a flow rate through the heat absorption loop 41 in the order of 23 gallons per minute is optimum with a flow rate through the heat transfer loop 28 of 16 gallons per minute.
Those flow rates will of course depend upon the nature of the heat exchanger 40 and the temperature of the environment T in which the heat exchanger 40 operates.
Fluid circulation in the heat absorption loop 41 may also enable a selective precooling or preheating of the fluid in the flow center 44. For example, when heating a dwelling, the fluid can be preheated in the flow center 44 from fluid circulation in the heat absorption loop 41 and when cooling a dwelling, the fluid can be precooled in the flow center from fluid circulation in the heat absorption loop 41.
A further embodiment of flow center is shown in FIGS. 4 and 5 in which like components will be denoted with like reference numerals with the suffix a added for clarity. Referring therefore to FIG. 4, the flow center 44 a includes a pair of cylindrical housings 50 a ₁ 50 a ₂. Each of the housings has a cap 52 a and vent valve 54 a. A balancing tube 60 interconnects the upper end of the housings 50 a to allow for fluid to flow between the housing.
Each of the housings 50 a receives the return from one loop and the supply to another of the loops. Thus, the housing. 50 a ₁receives fluid returned from the heat absorption loop 41 a through the pipe 38 a and supplies fluid to the heat transfer loop 28 a. Similarly, the housing 50 a ₂receives the return through pipe 38 a from the heat transfer loop 28 a and supplies fluid through the pipe 34, 36 a to the heat absorption loop 41 a.
The interconnection of the Units is shown in FIG. 5, from which it will be appreciated that the differential fluid returned from the heat absorption loop 41 a through the pipe 38 a may flow from the housing 50 a ₁through the bridge 60 to the housing 50 a ₂to supplement supply to the pump 42 a. Again, the pumps 30 a and 42 a will be sized to accommodate the optimum flow rates through the respective transfer loops.
A further embodiment of flow centre is shown in FIGS. 7 through 9 in which like reference numerals will be used for like components with a suffix “c” added for clarity. Flow centre 44 c can be used interchangeably with the flow centres 44, 44 a, 44 b shown in the previous embodiments. The flow centre 44 c has a cylindrical housing 50 c which is encompassed in an insulating foam 70 and encased in an outer casing 72. A cap 52 c is secured to the housing 50 c and has an upstanding square boss 76. A retaining bracket 78 is fitted over the cap and has a square hole 80 that fits around the boss 76. The bracket 78 is secured to the casing 72 by bolts 82 and thereby tamper proofs the cap by preventing unauthorized removal. The bracket 78 may also be used, after release of the bolts 82 and inversion of the bracket 78, as a wrench to remove the cap 52 c.
A pair of cross tubes 90, 92 extend diametrically through the housing 50 c and are sealed at the intersection of the tubes with the housing 50 c. Each end of the tubes 90, 92 is threaded to provide a connection with respective ones of the pipes 32 c, 34 c, 36 c, 38 c, as will be described in more detail below. Each of the cross tubes 90, 92 has an array of holes 94 at its midpoint. The holes 94 are evenly distributed around the circumference of the tube 90, 92 and in the embodiment shown there are four holes 94 equally spaced about the circumference. A greater or lesser number of holes 94 may be provided depending upon the particular circumstances. The aggregated cross section of the holes 94 is the same as or slightly greater than the cross section of the corresponding tube 90, 92.
As can be seen in FIG. 7, a sight glass 96 is provided on the exterior of the flow centre 44 c to provide an indication of the level of fluid contained within the flow centre 44 c. Conveniently, a spectrum indicating different colors of fluid corresponding to the approximate composition of the solution being circulated through the flow centre is provided alongside the sight level for easy reference and routine maintenance.
The tube 90 is connected between the return pipe 38 c of the heat absorption loop 41 c and the supply pipe 34 c of the heat transfer loop 28 c so that one end acts as an inlet from loop 41 c and the other as an outlet to loop 28. The tube 92 is similarly connected between the return pipe 32 c of heat transfer loop 28 c and the supply pipe 36 c of the heat absorption loop 41 c to provide respective inlets and outlets.
In operation, fluid from the heat absorption loop 41 c is delivered by the pump 42 c to the tube 90 where it flows from the return pipe 38 c to the supply pipe 34 c. Similarly, flow in the heat transfer loop 28 c from the pump 30 c is delivered to the tube 92 from the return pipe 32 c to the supply pipe 36 c of the heat absorption loop 41 c. The pumps 30 c, 42 c have a differential flow rate so that typically the flow delivered to the tube 90 from the absorption loop 41 c is greater than the flow rate extracted from the tube 90 by the transfer loop 28 c. The balance of the flow is discharged through the holes 94 in to the reservoir provided by the interior of the housing 50 c.
Similarly, the flow required from the tube 92 to supply the absorption loop 41 c is greater than that delivered by the return pipe 32 c of the transfer loop 28 c and therefore makeup fluid is provided through the holes 94 in the tube 92 from the housing 50 c. The holes 94 therefore provide for a cross flow between the heat transfer loop and absorption loop to maintain the desired flow rates as determined by the respective pumps.
The effect of the delivery of the fluid in the return pipe 38 c to the tube 90 is to supply it directly to the inlet to the pump 30 c, effectively supercharging the inlet to pump 30 c to a positive pressure, to ensure that it is operating under optimum conditions. The pump 30 c is not required to operate at a reduced inlet suction pressure, but at the same time ensures that the required flow rates between the two loops is maintained to provide optimum efficiencies.
The controller 25 is used to control operation of the heating system 10 and may be a simple thermostat interacting with the heat pump 18 to switch pumps 30, 42 on or off. However, as explained in greater detail below, the controller 25 may also be used to modulate operation of the pumps 30, 42. The pumps 30, 42 may be fixed flow rate pumps, or one pump may be variable and the other fixed. In the preferred implementation, each of the pumps 30, 42 is a variable flow pump to provide differing flow rates in the respective loops 28, 41. An example of such a pump and a suitable controller is a Danfoss VLT micro drive—FC51. The controller 25 provides a variable reference frequency to the motor of the pump which adjusts the rotational speed of the motor to match the reference frequency. Variable flow rates may also be provided by using a pair of pumps connected in series and selectively switching one of the pumps on or off.
The controller 25 in a preferred embodiment, is a programmable controller having outputs, namely Y₁, Y₂, and O. Outputs Y₁, Y₂control operation of the compressor 24 with Y₁calling for a first intermediate load, typically 67% of compressor capacity, and Y₂calling for a full, 100% load. The output O controls reversing valve 23 to switch between heating mode and cooling mode.
In general terms, the output Y₁is used to provide a reference frequency that sets the pump 30 at an intermediate flow rate, to match the required flow rate through the loop 28 when the compressor 24 has an intermediate load, and to maintain the pump 42 at a corresponding predetermined flow rate in excess of pump 32. Upon an output Y₂being received, when the compressor is conditioned to full load, the output of each pump 30, 42 is correspondingly increased to match the flow rates to the full load operating condition of the system.
The flow centre 44 c of FIG. 9 facilitates initial setup of the relative flow rates in the heating and cooling system 12, which, in turn, enhances control of the system 12 after the initial setup.
During initial setup, assuming a single, variable flow pump 30 c is used in the heat transfer loop 28 c, the pump 30 c is set to an'initial intermediate flow rate, typically that specified by the manufacturer of the heat pump 18. The flow rate is determined by measuring the pressure drop across the heat exchanger 26 c, after applying a correction factor to accommodate for varying temperatures of the fluid in the loop 28 c. A first set point x₁of the reference frequency is established for the required flow rate of pump 30 c. With the flow rate in loop 28 c established, the flow rate of the pump 42 c is adjusted to match that of the pump 30 c. This is facilitated in the flow centre 44 c by reducing the level of fluid through the drain port provided on the sight glass, so that the fluid is level with the upper cross tube 90. At this level, the relative flow rates in the loops 28 c, 41 c, can be observed from the flow through the cross ports 94. When the flows are equal, there is no net flow across the ports 94 and the flow rates are balanced.
Upon attaining a balanced flow, the pump 42 c is adjusted to increase the flow in the loop 41 c to achieve a nominally increased flow rate. It has been found that an increased flow rate of 5%-10% is satisfactory for typical installations. A first set point z₁of the reference frequency is established for the pump 42 c.
The demands of the heat pump 18 with the compressor 24 operating at full load require an increased flow rate in the loop 28 c. Accordingly, a second set point, x₂, is established for the increased flow rate required from pump 30 c, either empirically or by measuring the pressure drop across the heat exchanger 26 c as specified for a full load, and a corresponding set point z₂established for the pump 42 c. This may be done by observing net flows in the flow centre 44 or by extrapolation from the previous settings.
With the initial conditions established, the fluid is replaced in the flow centre 44. The controller 25 may then be used to control the pumps 30, 42 in normal use.
In one embodiment of the control strategy, as shown in FIG. 10, the outputs of controller 25 are used to adjust the flow rates from the pumps 30 c, 42 c, in the required ratio, to meet the demands of the system 12.
The output O determines the mode, heating or cooling, and upon the thermostat calling for an increase in temperature (in the heating mode), or a reduction of temperature (in the cooling mode), an output Y₁is applied to the compressor 24 and each of the pumps 30, 42.
The compressor 24 operates at the intermediate load (e.g. 67%) and the pumps 30, 42 circulate fluid at the rates determined by the set points x₁, z₁respectively.
If after a set period, 30 minutes to 120 minutes, the thermostat has not attained its required temperature, or if the thermostat calls for an immediate increase in temperature greater than 2° C., the controller 25 provides outputs Y₂to the compressor 24 and each of the pumps 30 c, 42 c.
The compressor 24 increases to full load and the output of pumps 30 c, 42 c, is increased to set points x₂, z₂respectively. The system 12 operates at these conditions until the required temperature is reached, or a further time limit is reached and the auxiliary heat is switched on by output W.
Upon attainment of the required temperature, the controller 25 removes the outputs Y₁, Y₂and W, and the system returns to an at rest condition, with the compressor and the pumps 30 c, 42 c switched off.
By matching the flow rates of the pumps 30 c, 42 c, to the demands of the compressor, the operation of the overall system may be optimized with the flow rates in the respective loops maintained in the required ratio.
It will be appreciated that the relative flow rates of the pumps 30 c, 42 c may be adjusted to suit a particular installation and system configuration with the set points for each pump chosen to provide the optimum flow rates.
The flexibility provided by the controller 25 and the use of a pump in each of the loops 28 c, 41 c, may be utilized to further optimize the operation of the system 12.
As shown in the schematic of FIGS. 11 and 12, different operating conditions are attained depending on the mode of operation.
In a heating mode, i.e. one in which heat is transferred in to the building 10, the set points z₁, z₂are selected so that the relative flow rate of the pump 42 c is increased beyond that needed to balance the flows in each loop. Typically a flow rate of 110% of that of the pump 30 c is found satisfactory, although flows in the range 105% to 125% may be used. The increased flow from pump 42 c is transferred through the flow centre 44 c between the cross tubes 90, 92, and is used to heat the fluid returning from the loop 28 c as it enters the loop 41.
The fluid delivered through loop 41 c to the loop 28 c will have a temperature approaching that of the ground source.
The fluid is transferred at that temperature to the inlet 34 c of the loop 28 c and delivered to the heat exchanger 26 c. Heat is extracted from the fluid for delivery to the building, resulting in a significant reduction of the temperature of the fluid. The fluid is returned at that temperature to the flow centre 44 c, where it is delivered through the cross tube 92 to the supply header 36 c.
Because of the reduced temperature, there is a risk, in some operating conditions, that localized freezing may occur, particularly on the surface of the header 36 c and heat exchanger 40 c, that impairs heat transfer. This is mitigated by the admixture of the excess flow from the pump 42 c with the return flow from the loop 28, which elevates the temperature of the fluid in the loop 41 c. With a flow rate of the pump 42 at 110% of pump 32, and a fluid temperature at around −5° C., it has been found that the overflow and admixture can elevate the fluid temperature by 2° C., sufficient to mitigate the surface freezing.
When operating in a cooling mode, i.e. when heat is rejected to the ground source, as shown in FIG. 12, the temperature of returning fluid is elevated. In this situation, admixture with the excess flow will reduce the temperature and reduce the rate of dissipation across the heat exchanger, which is undesirable. Accordingly, the pump 42 is controlled so that the flow differential is reduced and pump 42 is set to operate at a slightly greater flow rate, i.e. 2% greater than pump 32. In this case, the set points z₁, z₂are selected to minimize the cross over flow in the flow centre.
The control strategy, therefore, operates the pump 42 c to over supply the loop 28 c during heating mode to permit admixture, whereas in cooling mode the admixture is minimized by matching the outputs of pumps 42 c and 28 c.
During transient conditions, the variability of the flow rates may also be used to advantage and coordinated with the operation of the heat pump 18, as also shown in the schematics of FIGS. 11 and 12.
Assuming the building 10 is at the required temperature, the controller 25 maintains the heat pump 18 inactive and both pumps 32, 42 off, i.e. no flow.
When the controller 25 calls for heating, initially the fan and heat pump compressor associated with the building 10 is switched on as indicated as “C on at L1”. After a pre set delay, e.g. 5 seconds, a control signal Y₁is sent to the pump 30 c to initiate flow in the loop 28 c at the rate determined by the set point x₁. After a further delay. e.g. 20 seconds, the control signal Y₂is applied to the pump 42 to operate it at its maximum flow rate, i.e. at set point z₂and the pump 30 is maintained operating at the intermediate speed x₁. The increased flow rate is accommodated in the flow centre 41 and is maintained for an initial purge period, typically a period sufficient to provide a complete circulation of fluid in the loop 41, in the order of 300 seconds. A flow ramp up period of 30 seconds is provided to avoid sudden changes. If preferred, a higher flow rate than the set point z₂may be used for purging, but it is convenient to use the set point 22.
After the initial purge period, the control signal to the pump 42 reverts to Y₁and the output of the pump 42 will be ramped down over a period of 30 seconds, to set point z₁. The pump 30 is switched on at set point x₁. as the heating mode is selected, the set point z₁provides an over capacity providing admixture with fluid returning from loop 28.
If the required temperature is attained, the control signal Y₁is removed. The controller 25 asserts an output Y₂to the pump 42 for a shut down period, typically 300 seconds, to maintain circulation in the heat transfer loop 41. Thereafter, the flow rate is ramped down and the pump 42 switched off.
When the required temperature has not been attained after a preset interval, i.e. 30-120 minutes, the output Y₂is asserted to each of the pumps 32, 42 and both operate at their maximum respective rates, as determined by set points x₂and z₂. Once the temperature is attained, the pumps 32, 42 are shut down as described above.
A similar sequence is implemented in the cooling mode, with the set point z₂of pump 42 being the lower value that matches the maximum capacity of the pump 32.
The independent operation of the two pumps 32, 42, may therefore be used to establish optimum flow rates in each loop for steady state and transient conditions, without impacting on the design conditions for the heat pump 18.
It will be appreciated that the examples above are exemplary and other combinations may be used to meet the particular design parameters of the system 12.

Claims

1. A geothermal energy transfer system to transfer thermal energy between an energy source and an energy consumer, said system comprising a first loop to circulate heat transfer fluid through said source, a second loop to circulate heat transfer fluid through said consumer, a fluid reservoir connected to each of said loops to receive fluid from and deliver fluid to each of said loops, a first pump to circulate fluid in said first loop and a second pump to circulate fluid in said second loop.

2. The system of claim 1 wherein at least one of said pumps has a variable flow rate.

3. The system of claim 2 wherein both of said pumps have a variable flow rate.

4. The system of claim 2 including a controller to control the flow rate of said pumps.

5. The system of claim 4 wherein said controller controls a heat pump thermally connected to one of said loops and, said flow rates are coordinated with the operation of said heat pump.

6. The system of claim 1 wherein each of said loops has a supply and a return and the supply of one of said loops is connected to the return of the other said loops.

7. The system of claim 6 wherein said reservoir is connected between the supply and returns of each loop to accommodate differing flow rates therein.

8. The system of claim 7 wherein the supply and returns are connected to respective inlets and outlets of said reservoir.

9. The system of claim 8 wherein said reservoir has a pair of inlets and a pair of outlets and said pumps are connected to respective pairs of said inlets and outlets.

10. The system of claim 9 wherein an inlet connected to one of said loops is connected to an outlet connected to the other of said loops.

11. The system of claim 10 wherein each of said inlets and outlets is in communication with said reservoir.

12. The system of claim 1 wherein the flow rates of said first and second pumps are different and said reservoir accommodates the differential in flow.

13. The system of claim 12 wherein at least one of said first and second pumps is adjustable for flow rate.

14. The system of claim 13 wherein both of said pumps are adjustable for flow rate.

15. The system of claim 14 wherein operation of said first and second pumps is controlled by a controller.

16. The system of claim 15 wherein said controller adjusts said first and second pumps between a first condition in which both pumps have an intermediate flow rate and a second condition in which both pumps have a flow rate greater than said intermediate flow rate.

17. The system of claim 16 wherein said flow rates are maintained in a predetermined ratio in both said first and second conditions.

18. The system of claim 17 wherein said rates may be varied depending on the operational mode of said energy transfer system.

19. A flow centre for use in a geothermal energy transfer system, said flow centre comprising a reservoir to contain fluid, a first inlet for connection to a return of one loop and a supply of another to receive a differential flow through said loops, and an outlet for connection to a supply of said one loop and a return of said other loop to supply fluid to make up for a difference in flows in said loops.

20. A flow centre according to claim 19 wherein a pair of tubes extend through said reservoir to permit connection at opposite ends of said respective supply and return, said tubes having an aperture therein to provide respective ones of inlet and said outlet.

21. A flow centre according to claim 19 wherein a pair of reservoirs are provided and a conduit is provided to transfer fluid between said reservoirs.

22. A flow centre comprising a body defining a reservoir, a pair of tubes extending through said reservoir and having opposite ends for connection to respective pipes, and an aperture intermediate said ends to allow fluid communication between said tube and said reservoir.

23. The flow centre to claim 22 where said aperture is provided by a plurality of holes disposed about the circumference of said tube.